1. Field of the Invention
This invention relates to a fuel supply unit for supplying fuel to a fuel supply system of an engine from a fuel tank mounted on a vehicle such as a motorcycle.
2. Description of Background Art
Japanese Patent Laid-Open Publication No. Sho. 63-227949 discloses a fuel supply unit for a vehicle, in which a fuel tank houses a subsidiary tank, which encloses a fuel pump. A fuel return pipe communicates with the fuel pump via an open end thereof. FIG. 6 schematically illustrates the configuration of a fuel supply unit including an in-tank type fuel pump that is applied to a motorcycle.
Referring to FIG. 6, a fuel pump 2 is housed in a fuel tank 1 at a rear bottom thereof, and is connected at its inlet port 3 to a strainer 4 having a resin mesh filter for removing foreign matter. A discharge pipe extends from a discharge port of the fuel pump 2 for introducing fuel to a throttle body 7 outside the fuel tank 1 via a high pressure fuel filter 6. The fuel is then injected by fuel injectors into combustion chambers of the engine. Part of the fuel is returned as surplus fuel to an area near the strainer 4 by a pressure regulator 9 of the throttle body 7 via a connecting hose 10a and a fuel return pipe 10.
In the foregoing related art, the fuel returned via the fuel return pipe contains a lot of gases. The fuel pump draws up such returned fuel when the fuel in either the fuel tank or the subsidiary tank is nearly reduced to a lower limit. Therefore, the engine sometimes suffers from a surge. In such a case, the mesh filter in the strainer does not contribute to separation of gases from the fuel.
When accelerating, decelerating or turning, a motorcycle changes its posture extensively compared with a four-wheel vehicle. In such a case, the motorcycle engine tends to suffer from surge because the level of the fuel varies in the fuel tank. There has been a strong demand for preventing the surge caused by the foregoing reasons.